The present invention provides catalysts for oxidative dehydrogenation of hydrocarbons. It is directed to new catalyst system exhibiting very high olefin selectivity.
A number of oxidative dehydrogenation catalysts are known in this field such as U.S. Pat. Nos. 5,759,946 and 5,468,710; Japanese Patent Nos. 93150371, 07010782 A2 and 3-218327; German Patent No. 2, 124,438; and EP Patent No. 0557790 A2.
Olefinic hydrocarbons are very important intermediates in the petrochemical industry. Examples of commercial production interests include ethylene, propylene, butenes, isobutene, and styrene. Substantial efforts were directed towards the production of such compounds by conventional catalytic dehydrogenation. Conventional dehydrogenation has several disadvantages, such as the need of high reaction temperature (600-800xc2x0 C.), the catalyst deactivation by coke formation, the consequent need of periodic catalyst regeneration, and the thermodynamic limitation of the catalyst activity. These drawbacks can be avoided in the case of oxidative dehydrogenation (ODH), due to the presence of oxygen in the reaction mixture. However, to date there is no commercial catalyst system available for this purpose.
U.S. Pat. No. 5,468,710, relates to a composition containing sulfided nickel and non-acidic alumina and used as a normal dehydrogenation catalyst of organic compounds, e.g., isobutane to give isobutene.
Isobutene and methacrolein were prepared according to the JP 07010782 A2 by treatment of isobutane with molecular oxygen in the gas phase in the presence of oxidative dehydrogenation catalyst mainly containing Mo and Bi. Isobutane, oxygen and nitrogen gas mixture was passed through a reactor containing mixed oxide catalyst of molybdenum, bismuth, iron, cobalt, cesium and silicon and oxidative dehydrogenation catalyst containing nickel and phosphorous at 440xc2x0 C. to show 3.8% conversion and 13.9, 3.3 and 18.9% selectivity for isobutene, propene, and methacrolein, respectively.
Japanese Patent No. 93150371 relates to alkali metals and alkaline earth metals containing catalysts were used for preparation of isobutene and methacrolein from isobutane with oxidative dehydrogenation catalysts and mixed oxide catalysts containing bismuth and molybdenum.
German Patent No. 2,124,438 relates to an oxidative dehydrogenation of isobutane in the presence of hydrogen iodide. The conversion of isobutane was 28% and the selectivity to isobutene was 85%. The method, however, has the disadvantage of requiring the addition of hydrogen iodide.
The Japanese Patent relates to an oxidative dehydrogenation of propane or isobutane using a catalyst comprising tin oxide and phosphorous oxide as the main components. It also relates to a catalyst having indium oxide and phosphorous oxide as the main components. However, the selectivity is low; 32% at 1.4 conversion.
U.S. Pat. No. 5,759,946 relates to a catalyst based on chromium oxide for oxidative dehydrogenation of hydrocarbons.
EP Pat. No. 0557790 A2 relates a catalyst containing phosphorous oxide for producing isobutene by oxidative dehydrogenation of isobutane.
As seen from the above, it is a major challenge to achieve high conversion to olefin at high selectivity, i.e., to achieve maximum yield of the desired product, while minimizing the further oxidation activity. None of the cited references teaches or discloses a catalyst, which provides a high performance of the selective production of olefins from their corresponding paraffins. Accordingly, it would be desirable to produce an improved catalyst for use in the selective production of olefins from their corresponding paraffins.
It is an object of this invention to overcome the difficulties presented in the cited references for producing olefins as disclosed in the present application.
Another object of the invention is to provide a useful catalyst for producing olefins from hydrocarbons selectively by performing the oxidative dehydrogenation in the presence of a catalyst comprising bismuth, nickel and alumina.
The foregoing and other objects and advantages of the invention will be set forth in or will become apparent from the following description.
The present invention provides a new catalyst system comprising bismuth, nickel and alumina for the production of olefins by the oxidative dehydrogenation of hydrocarbons. The reaction can be carried out at low reaction temperature with no partial oxidation product formation. Such high selective catalyst may also find further application in the catalytic separation of hydrocarbons or in synergistic combinations with other reactions.
The catalyst including a catalytic composition having the atomic ratios described by the empirical formula set forth below:
BiaNi Ob/Al2O3
Where: a=0.001 to 0.5
b=the number of oxygen required to satisfy the valency requirements of the elements present
The numerical values of a and b represent the relative gram-atom ratios of the elements, respectively, in the catalyst composition, where b is a number required to satisfy the valence requirements of the other elements. The elements are present in combination with oxygen, preferably in the form of various oxides. Other objects as well as aspects, features and advantages of the present invention will be apparent from a study of the present specification, including the claims and specific examples.
One aspect of the invention teaches to a new catalytic system for the production of olefins from hydrocarbons via the oxidative dehydrogenation, in particular, for the production of isobutene from isobutane. More specifically, the present invention is directed to a highly selective catalyst comprising the atomic catalyst composition described by the empirical formula set forth below.
BiaNiOb/Al2O3
Where: a=0.001 to 0.5
b=the number of oxygen required to satisfy the valency requirements of the elements present
The catalyst of this invention is supported on alumina. However, other suitable supports including silica, titania, zirconia, zeolites, silicon carbides and others alone or as mixture can be used. The catalyst comprises usually 70-98% by weight alumina.
The following examples are illustrative of some of the products and methods of making and using the same falling within the scope of the present invention. They are, of course, not to be considered in any way limitative of the invention. Numerous changes and modifications can be made with respect to the invention. Illustrative examples were made for production of isobutene from isobutane.
The basic catalyst of the present invention is a mixed metal oxide catalyst, which could be prepared according to any procedure well known by a skilled person in the art. Methods used to prepare representative catalyst are given below.
As used in the following examples, the following terms are defined in the following manner:
1. xe2x80x9cW/Fxe2x80x9d is defined as the weight of the catalyst in grams divided by the flow rate of reactant stream in ml/sec measured at S.T.P.
2. xe2x80x9cIsobutane (i-C4H10) conversionxe2x80x9d is defined as:                     Mols        ⁢                  xe2x80x83                ⁢        i        ⁢                  -                ⁢                  C          4                ⁢                  H          10                ⁢                  xe2x80x83                ⁢        in        ⁢                  xe2x80x83                ⁢        feed            -              Mols        ⁢                  xe2x80x83                ⁢        i        ⁢                  -                ⁢                  C          4                ⁢                  H          10                ⁢                  xe2x80x83                ⁢        in        ⁢                  xe2x80x83                ⁢        effluent                    Mols      ⁢              xe2x80x83            ⁢      i      ⁢              -            ⁢              C        4            ⁢              H        10            ⁢              xe2x80x83            ⁢      in      ⁢              xe2x80x83            ⁢      feed        xc3x97  100  ⁢  %
3. xe2x80x9cIsobutene (i-C4H8) selectivityxe2x80x9d is defined as:             Mols      ⁢              xe2x80x83            ⁢      i      ⁢              -            ⁢              C        4            ⁢              H        8            ⁢              xe2x80x83            ⁢      in      ⁢              xe2x80x83            ⁢      effluent              Mols      ⁢              xe2x80x83            ⁢      i      ⁢              -            ⁢              C        4            ⁢              H        10            ⁢              xe2x80x83            ⁢      converted        xc3x97  100  ⁢  %
4. xe2x80x9cIsobutene (i-C4H8) yieldxe2x80x9d is defined as:             Mols      ⁢              xe2x80x83            ⁢      i      ⁢              -            ⁢              C        4            ⁢              H        8            ⁢              xe2x80x83            ⁢      formed              Mols      ⁢              xe2x80x83            ⁢      i      ⁢              -            ⁢              C        4            ⁢              H        10            ⁢              xe2x80x83            ⁢      in      ⁢              xe2x80x83            ⁢      feed        xc3x97  100  ⁢  %
The following conditions were employed:
reaction temperature: 250-450xc2x0 C.
catalyst: 1 gm (2.1 cc)
pressure: atmospheric
W/F: 0.8 sec.
feed composition: isobutane/oxygen/helium: 26.5/6.6/66.9 (mol %)
Calcined catalysts were pressed into pellets, then crushed to 20-40 mesh fraction. The catalysts were tested in fixed bed quartz reactor. In each test the catalyst was pretreated in a stream of a mixture of oxygen and helium for one hour at 400xc2x0 C. Then, the feed gas was passed through the reactor at desired temperature.
After reaching the steady state, the reactor effluent was analyzed by using a modem gas chromatograph (HP 6890), equipped with both FID and TCD detectors. Activity results were calculated according to the equations given above.